1. Field of the Invention
The present invention relates to a novel pressure sensitive adhesive label sheet comprising a label of a plastic film coated with a pressure sensitive adhesive layer. More particularly, it relates to a pressure sensitive label sheet comprising polyethylene film which shows excellent appearance when label marks are printed on it and can be handled smoothly in the process using an automatic labelling machine.
2. Description of the Prior Art
Beautiful labels are attached to many commercial containers for the purposes of advertisement, good appearance of design and the like.
The labels are generally attached to containers automatically by transferring the adhesive labels having a pressure sensitive adhesive material from a release paper of a label tape to the surface of the containers by using an automatic labelling machine. The label tape is generally prepared by temporarily attaching a label sheet of 25 to 250 .mu.m thickness having label marks printed on it to a release paper through a layer of a pressure sensitive adhesive material and then by cutting out the label sheet alone to the shape of the label.
A film of a rather stiff material, such as PET, PVC and the like, has been generally utilized for the pressure sensitive adhesive label because of easier operation of the labelling but a film of a soft material, such as polyethylene and the like, has not been utilized.
However, when a film of a rather stiff material, such as PET, PVC and the like, is utilized for a label on a soft flexible container, physical properties of the film cannot match the flexibility of the container and wrinkling and lifting are often formed. When they are formed, the shape of the label is deformed and the appearance of the printing is deteriorated.
For solving the problem, a pressure sensitive adhesive label made of a low density polyethylene film as a label for squeeze bottles was disclosed (U.S. Pat. Nos. 4,587,158; Re 32,929). Pressure sensitive adhesive labels generally tend to become more fragile when they are printed. When the printed pressure sensitive adhesive label of a low density polyethylene disclosed in the patent described above is attached to a substrate having flexibility, the label may be fractured because the printed label has a lower tensile strength and cannot follow the elongation of the substrate. This label has another problem that it causes difficulty in the operation of the automatic labelling machine because of the lower stiffness.
Conventional transparent polyethylene films have a problem that printed marks do not show up clearly when the label marks are printed on the film and the appearance as a label is inferior.